Smut particles, fine dust and exhaust gas particles of traffic are a source of pollution with undesired consequences on public health. In order to prevent the exhaust of such particles or in order to remove the exhausted particles, a number of methods are known in the art. For instance, smut filters and catalysts can be used in exhaust systems to reduce the exhaust of such particles. Nevertheless, there may still be some emission of those particles.
Other solutions are for instance described in U.S. Pat. No. 6,511,258 and JP2002069943. U.S. Pat. No. 6,511,258 describes a method for controlling the amount of ionized gases and/or particles suspended in the air above roads, streets, open spaces or the like. This is done by establishing an electrical field between the top layer of a road, street, open space or the like, and the ionized gases and/or particles. By controlling the electrical field the amount of ionized gases and/or particles can be controlled, which are attracted or repelled. The electrical field is established by making at least the top layer of the surface concerned electrically conductive and connecting it to earth or to one pole of an electrical voltage source. In order to make the surface electrically charged, a network of conductive metal or a piezoelectric material is employed under the top layer which is placed in contact with earth or a negative voltage source. The electrically charged top layer may also be composed of a coating which is laid on top of the entire or parts of the surface, for example in the form of road marking or the like. This solution provided by U.S. Pat. No. 6,511,258 is a rather complicated solution that has the disadvantage that only positively charged particles are caught at the surface. JP2002069943 describes a soundproof wall arranged at the side of a road which is constituted of a mesh internal wall capable of leading exhaust gas to the inside of the soundproof wall, an external wall arranged at the outside of the road, and a vibrating device housing particles in the space defined between the internal wall and the external wall and vibrating the particles in order to adsorb the suspended materials by static electricity generated among the particles. This is also a relatively complicated solution which has further the disadvantage that it may only remove particles that are present or have migrated into the wall and does not remove remote pollution particles.
U.S. Pat. No. 6,106,592 describes a gas cleaning process and apparatus for removing solid and liquid aerosols entrained in a gas stream. The gas to be treated is passed through a wetted, electrostatic ally charged filter media. The polarity of the electrostatic charge on the filter media is selected to enhance the removal of captured solid particles from the filter media. The apparatus is readily adaptable to a modular gas cleaning system configuration wherein varying numbers of the apparatus may be operated in parallel to provide a gas cleaning system of any desired gas flow capacity. Fields of 80-800 kV/m are applied.
DE19648182 describes that to homogenize the electric field in a filter channel, that is defined by two precipitation electrodes, of a filter structure for the separation of dust like or drop-shaped impurities from a flow of gas, corona electrodes are used. These are plate formed—e.g. designed with a central plate and with edge plates projecting on opposite sides and joining front and back in an obtuse angle—and have, on the front and back edge, an in each case continuous area of curvature produced by beading, with a radius of curvature of 2-5 mm. The areas of curvature show, throughout their length, an approximately uniform curvature and constitute the laterally most protuberant parts. By the average distance of consecutive areas of curvature and the formation of the same, the production of charge carriers for electrostatic cleaning can be controlled and, in particular, overproduction of the same, which favours back spray, can be prevented. Corona formation occurs exclusively during voltage impulses and only at the areas of curvature. A field of 240 kV/m is applied.
EP0808660 describes a dust collector which can collect dust, especially fine dust (submicron particles). The dust collector, which removes dust and/or mist contained in a gas, comprises a charging means for charging dust and/or mist contained in a gas, a spraying means for spraying the charged dust or charged mist or spraying a dielectric material to the charged dust or mist, an electric field forming means for forming an electric field for subjecting the dielectric material to dielectric polarization, and a collecting means for collecting the dielectric material which have arrested at least either of the charged dust and charged mist. A field of 500 kV/m is applied.